Particularly in motor vehicles, many different controllers are used today. In order to connect these individual electronic system components, bus systems are used, such as CAN (Controller Area Network) or FlexRay. In established bus systems, it is possible to transfer the controllers that are connected to the bus to a quiescent state with reduced power consumption when none of the controllers are required. In this case, however, it is then possible for all respective bus systems and controllers of a connected system to be put into the quiescent state or back into the active state again simultaneously. Even if only a single arbitrary controller is requested for communication on an arbitrary bus, all the others likewise need to be in an active state. Therefore, even controllers that are not required for communication in this period are consuming power.
As part of the reduction of CO2 emissions from vehicles, what is known as partial networking has therefore been developed. In this case, it is possible for individual controllers (node partial networking) or buses (bus partial networking) to be put to “sleep” or “awoken” as required. By way of example, it is thus possible for a trailer controller to remain switched off while there is no trailer on a vehicle, even when other controllers are required on a bus during this time. In this way, controllers consume power only when they are also really needed, and the total power consumption in the vehicle and hence CO2 emissions can be reduced.
EP 0 981 875 B1 describes such a bus system having a plurality of controllers that allows partial networking in order to reduce the average power consumption of an overall bus system having 30 controllers from 2.5 mA to approximately 1.6 mA.
A problem that arises with the introduction of such partial networking is that the controllers can now see any messages or message changes that are sent while they are switched on. Buffer-storing (caching) the values locally in the sleeping controller, that is to say buffer-storing the original or a copy thereof there in a buffer store, for example, as is generally frequently done in data processing, is not possible in this case. If messages were to be sent by other controllers in the system while a controller is sleeping, the controller would, upon being woken up, set out from the state that is stored in its buffer store (cache), which is possibly already outdated when it wakes up, however.